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Publication numberUS5734669 A
Publication typeGrant
Application numberUS 08/749,832
Publication dateMar 31, 1998
Filing dateNov 15, 1996
Priority dateFeb 6, 1995
Fee statusLapsed
Publication number08749832, 749832, US 5734669 A, US 5734669A, US-A-5734669, US5734669 A, US5734669A
InventorsXinxiong Zhang, Pin Hong, Bruce H. T. Chai, Michael Bass
Original AssigneeUniversity Of Central Florida
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
1.3 μm lasers using Nd3+ doped apatite crystals
US 5734669 A
Abstract
Laser pumping and flashlamp pumping of apatite crystals such as trivalent neodymium-doped strontium fluorapatite (Sr5 (PO4)3 F) emits efficient lasing at both 1.059 and 1.328 μm. The pump sources for the SFAP material doped with Nd3+ includes pulsed Cr:LiSrAlF6 tuned to approximately 805.4 nm. Alternatively, similar results occurred using a continuous wave laser source of Ti:sapphire tuned to approximately 805.4 nm. A preferred embodiment includes a resonant cavity with a high reflectivity mirror having a reflectivity of 100% and an output coupler mirror with a reflectivity of less than 100%. An optional tuning component such as a Pockels Cell-Polarizer combination can also be included. The SFAP material doped with Nd3+ exhibits a large absorption cross section, high emission cross section, and long radiative lifetime.
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Claims(5)
We claim:
1. A method of simultaneously lasing an apatite crystal at 1.06 and 1.3 μm, comprising the steps of:
(a) emitting optical radiation from a pump source the pump source being tuned to approximately 805.4 nm chosen from one of a pulsed Cr:LiSrAlF6 laser and a continuous wave Ti:Sapphire laser; and
(b) pumping a gain medium in a resonator cavity with the optical radiation, the gain medium composed of trivalent neodymium-doped strontium: fluorapatite crystal (SFAP doped with Nd3+), the crystal being antireflection coated at both 1.06 and 1.3 μm; and
(c) extracting simultaneous peak emissions having wavelengths of approximately 1.06 and approximately 1.3 μm from the resonator cavity.
2. The method of simultaneously lasing an apatite crystal of claim 1, wherein the resonator cavity includes:
a first reflectivity mirror having a reflectivity of approximately 100%;
a Q-switch chosen from at least one of: a pockels cell-polarizer, mode locker, and an etalon, the Q-switch positioned between the first reflectivity mirror and the gain medium; and
an output coupler mirror having a reflectivity of less than approximately 100% connected to the gain medium.
3. A laser system for simultaneously outputting peak wavelength emissions of 1.06 and 1.3 μm comprising:
an excitation laser source for generating optical radiation, the laser source being tuned to approximately 805.4 nm chosen from one of a pulsed Cr:LiSrAlF6 laser and a continuous wave Ti:Sapphire laser;
a gain medium in a resonator cavity, the gain medium composed of an apatite crystal chosen from one of: Nd3+ :Sr5 (PO4)3 F, Nd3+ :Ca5 (PO4)3 F and Nd3+ :Sr5 (VO4)3 F, the crystal being antireflection coated at both 1.06 and 1.3 μm, the gain medium being pumped by the generated optical radiation; and
means for outputting peak wavelength emissions of approximately 1.06 and 1.3 μm from the resonator cavity.
4. The laser of claim 3, wherein the resonator cavity includes:
a first reflectivity mirror having a reflectivity of approximately 100%;
a Q-switch chosen from at least one of: a pockels cell-polarizer, mode locker, and an etalon, the Q-switch positioned between the first reflectivity mirror and the gain medium; and
an output coupler mirror having a reflectivity of less than approximately 100% connected to the gain medium.
5. A laser system for simultaneously outputting peak wavelength emissions of 1.06 and 1.3 μm comprising:
an excitation laser source for generating optical radiation, the laser source being tuned to approximately 805.4 nm chosen from one of a pulsed Cr:LiSrAIF6 laser and a continuous wave Ti:Sapphire laser;
a gain medium in a resonator cavity, the gain medium composed of trivalent neodymium-doped strontium fluorapatite crystal (SFAP doped with Nd3+), the crystal being antireflection coated at both 1.06 and 1.3 μm, the gain medium being pumped by the generated optical radiation; and
means for outputting peak wavelength emissions of approximately 1.06 and 1.3 μfrom the resonator cavity.
Description

This application is a continuation of application Ser. No. 08/383,954, filed Feb. 6, 1995, now abandoned.

This invention relates to apatite crystaline laser materials, and in particular to trivalent neodymium-doped strontium fluorapatite (SFAP) with high efficiency lasing at 1.059 and 1.328 μm.

BACKGROUND AND PRIOR ART

Solid-state lasers based on rare-earth doped crystal have been becoming substantially more significant. These types of systems are increasingly becoming more common in industrial, medical, scientific and military applications. The diverse nature of applications requires the availability of wide ranges of varieties of laser materials that can operate over wide wavelengths. However, most crystal materials are limited to operation over narrow ranges of wavelengths. For example, Nd-doped Y3 AL5 O12 (Nd:YAG) is the most common type of laser material, owing to its high emission cross section, relatively long energy storage time, and robust thermomechanical properties. The usual output wavelength for Nd:YAG is approximately 1.064 μm. Other crystal materials have also been doped with Nd and are limited in wavelength operation.

SFAP crystals doped with neodymium, Nd, also referred to as Sr5 (PO4)3 F and neodymium-doped strontium fluorapatite were successfully grown more than twenty years ago. See U.S. Pat. Nos. 3,504,300; 3,505,239; and 3,617,937 each to Mazelsky et al., which are each incorporated by reference. These references described that SFAP and other apatite crystals such as Calcium Fluorapatite(FAP), Ca5 (PO4)3 F grown at that time some twenty years ago were limited in lasing at approximately 1.059 μm. U.S. Pat. No. 5,341,389 to Payne et al. issued in August of 1994, which is also incorporated by reference, further described another apatite crystal Sr5 (VO4)3 F (SVAP) that exhibits lasing at approximately 1.059 μm.

SUMMARY OF THE INVENTION

The first objective of the present invention is to provide SFAP crystal doped with trivalent neodymium, Nd3+ that exhibits efficient lasing at approximately 1.3 μm.

The second object of this invention is to provide an SFAP crystal material doped with trivalent neodymium, Nd3+ that exhibits efficient lasing approximately at both 1.059 and 1.3 μm.

The invention includes laser and flashlamp for pumping apatite crystals such as trivalent neodymium-doped strontium fluorapatite (Sr5 (PO4)3 F) that lases approximately at both 1059 and 1.3 μm. The laser sources include pulsed Cr:LiSrAlF6 tuned to approximately 805.4 nm. Alternatively, similar results occurred using a continuous wave laser source of Ti:sapphire tuned to approximately 805.4 nm. Alternatively, lasing occurred using a flashlamp pump source. A preferred embodiment includes a resonant cavity with a high reflectivity mirror having a reflectivity of 100% and an output coupler mirror with a reflectivity of less than 100%. An optional timing component such as a Pockels Cell-Polarizer can also be included.

Further objects and advantages of this invention will be apparent from the following detailed description of a presently preferred embodiment which is illustrated schematically in the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the π and σ room temperature polarized absorption spectra of Nd3+ :SFAP in the 800 nm region.

FIG. 2 shows the π and σ room temperature polarized emission spectra of Nd3+ :SFAP in the 1.06 and 1.3 μm region obtained by continuous wave excitation at 805.4 nm.

FIG. 3A shows the plot of the laser output energy of Nd3+ :SFAP and Nd3+ :YVO4 for the pulsed operation.

FIG. 3B shows the plot of the laser output power of Nd3+ :SFAP and Nd3+ :YVO4 for continuous wave operation.

FIG. 4A shows the plot of the laser output energy as a function of the flashlamp energy of Nd3+ :SFAP at 1059 nm.

FIG. 4B shows the plot of the laser output energy as a function of the flashlamp energy of Nd3+ :SFAP at 1328 nm.

FIG. 5A shows the plot of laser output energy of Nd3+ :SFAP in Q-switched operation at 1059 nm.

FIG. 5B shows the plot of laser output energy of Nd3+ :SFAP in Q-switched operation at 1328 nm.

FIG. 6 is a schematic diagram of a Nd3+ :SFAP laser in Q-switched operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Before explaining the disclosed embodiment of the present invention in detail it is to be understood that the invention is not limited in its application to the details of the particular arrangement shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation.

The trivalent neodymium-doped strontium fluorapatite crystal (Nd3+ doped SFAP) or Nd3+ :Sr5 (PO4)3 F can be synthetically grown utilizing known techniques such as the Czochralski method similar to the one disclosed in U.S. Pat. Nos. 3,504,300; 3,505,239; and 3,617,937 each to Mazelsky et al., which are each incorporated by reference. Here an SFAP sample containing 0.68 at. % Nd3+ (11.41019 Nd3+ ions/cm3 ) was used for laser-pumped laser testing with a peak absorption coefficient of 25.7 cm-1.

Room temperature polarized absorption spectra of Nd3+ :SFAP in the 800 nm region are given in FIG. 1. The peak absorption coefficient is 2.74 cm-1 for a sample containing 0.2 mole % Nd3+ in the melt. Since the distribution coefficient of Nd3+ ions in SFAP is 0.36,1 the actual Nd3+ concentration in this crystal is approximately 0.072 at. %. As a result, Nd3+ :SFAP has an absorption cross section of 2.2610-19 cm2.

Room temperature polarized emission spectra of Nd3+ :SFAP are shown in FIG. 2. In FIG. 2, the emission is partially polarized with the π polarization stronger than the σ polarization with Room temperature emission decay of 0.072 at. % Nd3+ :SFAP is exponential with a decay time of 298 μs.

Here an SFAP sample containing 0.68 at. % Nd3+ (11.41019 Nd3+ ions/cm3 ) was used for laser-pumped laser testing with a peak absorption coefficient of 25.7 cm-1. The room temperature emission decay from the 4 F3/2 manifold is non-exponential in this sample, and, by normalizing the fluorescence intensity at t=0 to one and then integrating the entire decay curve over time, the decay time was found to be only 190 μs. This indicates the existence of concentration quenching in this SFAP crystal. The decay time measurements were done with fine-ground powders of SFAP crystals to avoid the decay time lengthening effect of self-absorption.

For laser experiments, a 1.9 mm-long sample of the 0.68 at. % Nd3+ :SFAP crystal was cut with flat and parallel faces containing the c-axis. Both pulsed and continuous wave (cw) laser-pumped-laser experiments were performed which simulated diode laser pumping. Pulsed laser action was excited with a long pulse Cr:LiSrAlF6 (Cr:LiSAF) laser. The Cr:LiSrAlF6 laser was tuned to the Nd:SFAP absorption peak at 805.4 nm with a spectral bandwidth of approximately 1 nm. Continuous wave (cw) excitation was achieved with a CW Ti:sapphire(continuous wave titanium saphire) laser tuned to 805.4 nm with a spectral bandwidth of approximately 0.1 nm. More than 95% of the pump power was absorbed in both pump schemes. The laser resonator was composed of a 5 cm radius of curvature high reflectance (HR) mirror coated for the wavelength of interest and a flat output coupler (OC) with a transmission up to 5%. The pump light was focussed with a 10 cm focal length lens through the HR mirror to a point near the side of the laser crystal facing the output coupler (OC).

Nd3+ :SFAP produced lasing that is linearly polarized along the c axis and occurs at 1.0594 μm for the 4 F3/2 to 4 II1/2 transition. Table I lists the thresholds and slope efficiencies for both the pulsed and continuous wave operations comparing Nd:SFAP at 1.0594 μm and Nd:YVO4 at 1.0646 μm. Table I compares these different crystals for output coupler (OC) transmissions of 1.2, 3 and 5%.

              TABLE 1______________________________________threshold         slope efficiency (%)pulsed (μJ)           cw (mW)    pulsed   cwT (%)SFAP   YVO4               SFAP YVO4                          SFAP YVO4                                     SFAP YVO4______________________________________1.2  5      3       4    4     40   34    42   413    6      4       5.5  4.6   54   49    54   535    9      6       6    6     60   54    59   59______________________________________

FIG. 3A shows the plot of the output energy of Nd3+ :SFAP and Nd3+ :YVO4 for the pulsed operation. In FIG. 3A, the laser output energy is plotted as a function of absorbed energy for a 5% Output Coupler (OC). FIG. 3B shows the plot of the output power of Nd3+ :SFAP and Nd3+ :YVO4 for continuous wave operation. In FIG. 3B, the laser output power is plotted as a function of absorbed power for a 5% Output Coupler (OC). The measured slope efficiency can be expressed as a function of the transmission of the OC, T, in equation (1) as follows:

η=ηoT/(T+L),                                       (1)

where ηo is the intrinsic slope efficiency; and L is the double-pass passive loss. In Table I, the parameters ηo=71% and L=0.93% can be used for pulsed operation, and ηo=64% and L=0.62% can be used for continuous wave (cw) operation for Nd:SFAP.

The performance of the Nd:SFAP was assessed by comparing Nd:SFAP with a 2.7 mm-long Nd:YVO4 crystal purchased from ITI Electro-Optics Corp. The emission decay time of Nd3+ ions in the Nd:YVO4 crystal was measured to be 98 μs, which is about the same as its radiative lifetime indicating negligible concentration quenching. The Nd:YVO4 crystal has a peak absorption coefficient of 17.4 cm-1 at 808.7 nm. The Nd3+ number density was estimated to be 71019 ions/cm3 according to the absorption data. The laser output was π-polarized and occurred at 1.0646 μm. However, the laser output power varied from region to region in the crystal indicating inhomogeneities. The results obtained from the best performing region are summarized in Table I for comparison.

The Nd:YVO4 laser input/output characteristics are also given in FIG. 3A and FIG. 3B for a 5% OC. While the Continuous Wave (cw) performances for both crystals are almost identical, the pulsed slope efficiencies for YVO4 are slightly lower than those for SFAP. Analysis of the slope efficiency as a function of the OC transmission for Nd:YVO4 yields ηo=68% and L=1.18% for pulsed operation, and ηo=64% and L=0.67% for cw operation.

The stimulated emission cross section of Nd:SFAP has been estimated by the inventors hereof to be 5.410-19 cm2 at 1.059 μm5 . As a result, the product of the stimulated emission cross section and the radiative decay time for Nd:SFAP is about 1.5 time that of Nd:YVO4. Concentration quenching exists in the SFAP crystal used in the lasing experiment but was negligible in the tested Nd:YVO4 sample. However, both crystals performed almost identically at 1.06 μm lasers in our experiments. Thus, it is more than probable that SFAP will outperform YVO4 for comparable Nd3+ concentrations.

FIG. 2 shows that the relative branching ratio of the 4 F3/2 to 4 II3/2 transition at around 1.3 μm to the 4 F3/2 to 4 II1/2 transition at around 1.06 μm is quite high. The ratio of the peak intensities at 1.3279 and 1.0594 μm was measured to be 0.37. The similar ratio is only 0.24 in Nd:YVO4 which is known to be a 1.3 μm laser. Lasing at 1.3 μm was tested using the same setup described above except for the coatings. Both mirrors of the resonator in this case have high transmissions (approximately 90%) at around 1.06 μm. The crystal was anti-reflection coated at both 1.06 and 1.33 μm. Lasing was π-polarized and occurred at 1.3279 μm.

Again, FIG. 3A shows the plot of the output energy of Nd3+ :SFAP for the pulsed operation. In FIG. 3A, the laser output energy is plotted as a function of absorbed energy for a 5% Output Coupler (OC). FIG. 3B shows the plot of the 1.3 μm laser output power of Nd3+ :SFAP for continuous wave operation. In FIG. 3B, the laser output power is plotted as a function of absorbed power for a 5% Output Coupler (OC). The cw threshold and slope efficiency are 14 mW and 46%, respectively. In pulsed operation the threshold and slope efficiency are 22 μJ and 52%. The quantum limited slope efficiency is approximately 60% for the 1.33 μm transition and thus it is clear that Nd:SFAP performs well as a 1.33 μm laser. By comparing the thresholds at 1.059 and 1.328 μm the effective stimulated emission cross section at 1.328 μm was estimated to be not less than 2.310-19 cm2.

FIG. 4A shows the plot of flash/amp output energy of Nd3+ :SFAP at 1059 nm in flashlamp pumped laser operation. FIG. 4B shows the plot of laser output energy of Nd3+ :SFAP at 1328 nm in flashlamp pumped laser operation. Referring to FIGS. 4A and 4B, it is apparent that 2.7 J for 1.059 μm and 1.8 J for 1.328 μm have been obtained.

FIG. 5A shows the plot of laser output energy of Nd3+ :SFAP in Q-switched operation for 1059 nm. FIG. 5B shows the plot of laser output energy of Nd3+ :SFAP in Q-switched operation for 1328 nm. From FIGS. 5A and 5B, it is apparent that 150 mJ for 1.059 μm and 100 mJ for 1.328 μm have been obtained.

FIG. 6 is a schematic diagram of a Nd3+ :SFAP pump in Q-switched operation. Laser source or flashlamp 100 can be a pulsed or continuous laser pump or flashlamp as described above, for pumping laser medium, 200,SFAP which is positioned within a cavity formed from mirrors 300 and 600. The mirrors need be reflective at 1.3 μm and not be antireflective at 1.06 μm in order to have an output of 1.3 μm. Prior art devices require additional layers and thicknesses of dielectric layers on the mirrors and the like in order to restrict the 1.06 μm emission so that only a 1.3 μm emission occurs. Mirror 300 refers to a high reflection mirror with a reflectivity of approximately 100%. Components 400, 500 are the Q-switch device such as a Pockels Cell-Polarizer combination, mode-locker, etalon, and other known types of shutters. 600 refers to Output Coupler (OC) mirror having a reflectivity of less than 100%. Although, pump source 100 is shown as transverse mounted, source 100 could pump longitudinally through high reflection mirror 300.

Although the preferred embodiments described above refer to specific types of pulsed and continuous wave laser sources, and a flashlamp, other laser sources such as but not limited to diode laser source can be used.

Applications using 1.3 micrometer lasers based on the invention include but are not limited to fiber optic communications and cable television using the fundamental frequency, high power frequency doubled lasers for photo-dynamic therapy, frequency conversion based on 1.3 μm and dual wavelength lasers.

While the invention has been described, disclosed, illustrated and shown in various terms of certain embodiments or modifications which it has presumed in practice, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3504300 *Oct 3, 1966Mar 31, 1970Westinghouse Electric CorpFluorapatite laser material doped with neodymium and manganese
US3505239 *Jul 26, 1966Apr 7, 1970Westinghouse Electric CorpCrystal laser material
US3549552 *Jan 27, 1969Dec 22, 1970Westinghouse Electric CorpCalcium halophosphate "daylight" phosphor
US3617937 *Jul 18, 1969Nov 2, 1971Westinghouse Electric CorpLaser containing neodymium-doped calcium fluoroapatite laser crystal
US3627692 *May 28, 1968Dec 14, 1971Westinghouse Electric CorpFluoroapatite laser material doped with holmium or thulium and chromium
US3869403 *Jan 11, 1973Mar 4, 1975American Optical CorpNeodymium doped acetate glass exhibiting fluorescence at 1.06 micrometers
US4038204 *May 3, 1968Jul 26, 1977Westinghouse Electric CorporationAlkaline-earth metal halophosphate luminescent composition activated by divalent europium and method of preparing same
US4075532 *Jun 14, 1976Feb 21, 1978General Electric CompanyCool-white fluorescent lamp with phosphor having modified spectral energy distribution to improve luminosity thereof
US4266160 *Jun 22, 1979May 5, 1981Gte Products CorporationStrontium-calcium fluorapatite phosphors and fluorescent lamp containing the same
US4266161 *Jun 22, 1979May 5, 1981Gte Products CorporationCool white lamp using a two-component phosphor
US4731795 *Jun 26, 1986Mar 15, 1988Amoco CorporationSolid state laser
US4765925 *Mar 16, 1987Aug 23, 1988Mitsui Mining & Smelting Co. Ltd.Solid state laser hosts
US4782491 *Apr 9, 1987Nov 1, 1988Polaroid CorporationIon doped, fused silica glass fiber laser
US4884277 *Jun 16, 1988Nov 28, 1989Amoco CorporationFrequency conversion of optical radiation
US4933947 *May 18, 1989Jun 12, 1990Amoco CorporationFrequency conversion of optical radiation
US4956843 *Oct 10, 1989Sep 11, 1990Amoco CorporationSimultaneous generation of laser radiation at two different frequencies
US5022041 *Oct 6, 1989Jun 4, 1991Spectra-PhysicsNear resonant Nd3+, solid state laser system
US5022043 *Dec 20, 1989Jun 4, 1991Spectra-PhysicsHigh power diode-pumped solid state laser with unstable resonator
US5031182 *Oct 2, 1989Jul 9, 1991Amoco CorporationSingle-frequency laser of improved amplitude stability
US5130997 *Dec 18, 1990Jul 14, 1992LaserscopeMedical laser apparatus, high powered red laser used in same, and laser resonator with non-linear output
US5216681 *Aug 5, 1991Jun 1, 1993Trw Inc.Highly-efficient solid-state blue laser
US5280492 *Nov 15, 1991Jan 18, 1994The United States Department Of EnergyYb:FAP and related materials, laser gain medium comprising same, and laser systems using same
US5309452 *Jan 31, 1992May 3, 1994Rutgers UniversityPraseodymium laser system
US5341389 *Jun 8, 1993Aug 23, 1994The United States Of America As Represented By The United States Department Of EnergyYtterbium- and neodymium-doped vanadate laser hose crystals having the apatite crystal structure
US5517516 *Jan 21, 1994May 14, 1996The Regents Of The University Of CaliforniaOptically pumped cerium-doped LiSrAlF6 and LiCaAlF6
Non-Patent Citations
Reference
1Bethea; "MegawattPower at 1.318 in Nd +3:YAG and Simultaneous Oscillation at Both 1.06 and 1.318 .IEEE Journal of Quantum Electronics,Feb.1973,p. 251.
2 *Bethea; MegawattPower at 1.318 in Nd 3:YAG and Simultaneous Oscillation at Both 1.06 and 1.318 .IEEE Journal of Quantum Electronics,Feb.1973,p. 251.
3 *Zhang et al. Efficient Laser Performance of Nd3 , Sr5(PO4)3F at 1.059& 1.328um, OSA Proceedings, Advanced Solid State Lasers vol. 20, Feb. 7 10, 1994, pp. 53 55.
4Zhang et al. Efficient Laser Performance of Nd3+, Sr5(PO4)3F at 1.059& 1.328um, OSA Proceedings, Advanced Solid-State Lasers vol. 20, Feb. 7-10, 1994, pp. 53-55.
5 *Zhang et al., Efficient Laser Performance of Nd3 :Sr5(PO4) 3F at 1.059 & 1.328um, Appl. Phys. Lett. 64(24), 13 Jun. 1994, pp. 3205 3207.
6Zhang et al., Efficient Laser Performance of Nd3+:Sr5(PO4) 3F at 1.059 & 1.328um, Appl. Phys. Lett. 64(24), 13 Jun. 1994, pp. 3205-3207.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US6587496 *Dec 11, 2000Jul 1, 2003Lite Cycles, Inc.Single-mode pump power source
CN101063231BApr 25, 2006May 9, 2012中国科学院福建物质结构研究所Chromium doped molybdic acid aluminum potassium tunable laser crystal
Classifications
U.S. Classification372/41, 372/23
International ClassificationH01S3/16
Cooperative ClassificationH01S3/1611, H01S3/16, H01S2303/00, H01S2302/00, H01S3/1645
European ClassificationH01S3/16
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Effective date: 20100331
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